Drafting instrument



Feb, 187 1941, s. MCF. coFr-'MAN Erm. l

DRAFT ING INSTRUMENT Filed Maren 2. 1940 Patented Feb. 18, 1941 UNITED STATES DRAFTIN G INSTRURiENT Samuel McFarland Coffman and J ames Edwin Bell, Jr., Kansas City, Mo.; said Coffman assignor to said .l ames Edwin Bell, Jr.

Application March 2, 1940, Serial No. 321,960

1o claims. y(c1. ca -177) I This invention relates to engineering instruments and particularly todrafting equipn'lentl in the nature of a drafting instrument, and the primary .object is to provide a simple, durable and easily manipulated device which may be employed in describing arcs of a true circle.

One of the important aims of this invention is the provision of a circular drafting instrument which has means visible to the operator, for indicating the degrees .of the arc described with relation to four different scales of measurement, each of which is customarily employed in plotting curves most commonly used by engineers.

A yet further aim of the instant invention is to provide a drafting instrument of the aforementioned character wherein is provided a pair of specially disposed rotatable plates, each of which actuates a plurality of connecting rods joined to a flexible strip that is deformed from a normal condition to produce the desired arc as the manually controlled operating means for the aforesaid plates is manipulated.

A still further object of the instant invention is to provide an inexpensive, light, convenient,

and unique drafting instrument, usable in plotting curves and for indicating the degrees .of the curves in terms based upon a number of commonly used scales of measurement.

This invention has Afor a further object the provision of a drafting instrument of the aforementioned character wherein isY incorporated a compensating track for moving the ends of a number of rods toward and from a common center about which they are being rotated as such rotation occurs. v

Other objects of the invention will occur to one skilled in the art when the preferred embodiment of the invention is understood through a reading of the following specification, which refers to the accompanying drawing wherein:

Figure 1 is a top plan view of a drafting instrument, made in accordance with the present invention, parts ybeing broken away for clearness.

Fig. 2 is an inverted fragmentary elevational view yof the drafting instrument.

Fig. 3 is a vertical cross sectional view taken on line III-III of Fig. 1.

Fig. 4 is a fragmentary detailed sectional view taken on line IV-IV .of Fig. k1.

Fig. 5 is a fragmentary cross sectional view taken on line V-V of Fig. 2; and

Fig. 6 is a similar view through a portion of one of the connecting rods taken .on line VI-VI of Fig. 2.

1n the preferred form of the invention, a flexible strip l forms a` guiding edge for the drafting instrument after the same has been deformed and bent to create an arc of a circle through the medium `of a plurality of connecting rods l2. 5y Strip Ill is mounted upon a body I4 in the nature of a case through the upper wall I6' of which is formed a number of sight openings I8, through which to View an underlying scale 2l) having indma 22 thereon.l 10

Body I4 is in the form of a plate or planar element having notches 24 formed inwardly `from the arcuate edge thereof to accommodate certain parts of the connecting rods I2.

A nose block 26 carried by body I4 is bifur- 15 cated at its outermost part and receives transverse lug 28 to hold strip l@ in place. VA pin 30 is employed to secure lug 28 and nose block 25 in assembled relation. Nose block 26 engages Y. strip l@ at a point intermediate its ends and 2 preferably at a place midway between the free ends thereof so that balance may occur, and further, so that connecting rods I2 on each side of nose block 25, may operate eiciently. In practice it has been found desirable to use a stripsubstantially 18 inches long.

The ends of connecting rods I2 are secured to strip I0 through the medium of a yoke 32 and. turn-buckle 34. Yoke 32 has a screw-threaded stem 3G extending into turn-buckle 34 and one end of connecting rod I2 is screw-threaded in a direction opposite to the threads on stem 36 which likewise projects intcvturn-buckle 34 so thaty the length of the respective connecting rods ,35 may be altered to adjust strip I0. y

.The legs of yoke 32 embrace an ear 38 secured to one side of strip I0 and a pin 40 pivotally secures together yoke 32 and ear 38. When the rear face of strip Ill is drawn against the edge of body I4, yoke 32 nds clearance by entering a notch 24.

A vertical spindle-42 is mounted on body I4 with the ends thereof disposed on opposite sides of said body to support the upper plate 44 and 5 alower plate 45. These plates are pivotally mounted upon spindle 42 for free movement about the axis thereofand upper plate 44 has a gear segment 48 formed thereon, while a gear segment 5D is created .on plate 46. A pinion 52 50 pivotally mounted upon axle 54 is in mesh with gear 'segments 48 and 50 so that as one plate is rotated about the axis of spindle 42, the other plate will move about said axis in an opposite direction. v 55 Scale 26 is mounted upon spindle 42 for movement therewith and in the same direction as upper plate 44.

Each plate 44 and 46 respectively is reduced in width to form a stem 56 and 58 respectively. It is to this portion of the plates that the inner ends of connecting rods I2 are secured.

As illustrated in Figs. 4 and 5, connecting rods I2 are not directly secured to these stem portions 56 and 58 respectively but are slidably mounted thereon through the medium of a tubular element 66 and 62 respectively. Upper plate 44, for example, has tubular element 66 mounted thereon as illustrated in Fig. 4. The inner ends of connecting rods I2 are joined to element 60 by screws or analogous means 64 and an operating lever 66 is attached to stem portion 56. Lever 66 has its inner end pivotally secured to spindle 42 while the outer end thereof is notched as at 68 to ride over `an arcuate track 'I0 concentric with the axis of spindle 42. If desired, the outer end of this operating lever` 66 may have means for securing the same in place along track 'I8 and since any desirable mechanism may be employed for this purpose, the same is not here detailed but shown to be a housed clutch engaging track l0 and operated by exposed buttons 'I2.

A compensator must be included in the instrument because the path of travel followed by any one of the points of connection between elements 60 and 62 and the several connecting rods I2, is not a true arc but a path of travel having different radii as the strip is flexed to form arcs of diiferent degrees.

The effective lengths of rods I2 are changed as plates 44 and 46 are moved about their common axis of rotation. To accomplish this end, the tubular element 60 to which is attached arms I2 on one side of nose 26, is moved toward and from spindle 42 through the medium of guide 14. This guide 'I4 has a slot I6 provided therein and block 78 pivotally mounted as at 80 to tubular element 6I) rides in slot 16. Slot 'I6 is not concentric with spindle 42 and therefore, as operating lever 66 is manually manipulated, the effective length, and therefore the action by rods I2 upon strip I0, will be altered to dispose said strip ID in a proper position as curves of different degrees are formed.

Lower plate 46 is formed in precisely the same manner as upper plate 44 in that i-t has an eX- tended portion 58 slidably retained in tubular element 62. Arms I2 on the opposite side of nose 26 from those carried by member 56, yare attached to member 62 so that as plate 46 is rotated about the axis of spindle 42, tubular element 62 will be moved toward and from spindle 42 to create the proper effect upon rods I2 so as to produce a curve having an accurate radius.

Lower tubular element 62 has a block 82 mounted thereon to ride in slot 84 of guide 86. This guide 86 is on one side of body I4 while guide 'I4 is mounted on the opposite side thereof. Feet 88 support the instrument upon the surface being worked on and the lower edge of strip I8 is relatively close to this surface so that a pencil or the like may be drawn along the front side of strip Il! after it has been positioned to present the curve desired.

It is desirable to use scales of 1 in. to 100 ft., 1 in. to 200 ft., 1 in. to 300 ft., and l in. to 400 ft. The indicia 82, visible through windows I8 of the upper wall I6, will indicate to the operator the degree of curve with respect to these several scales of measurement and any suitable designations visible through these windows may be marked upon the underlying flat scale 28-. Numerals 23 on wall I6 adjacent to each window I8, indicate the particular scale to which the underlying indicia 22 relates.

Light materials should be used in producing the instrument and since it is to be employed on a drawing board, the operating means is coniined to a single element that may be manipulated by one hand.

This application is a continuation in part of a case previously filed by James E. Bell, Jr., Serial No. 278,054, filed June 8, 1939, covering improvements for Curve plotting instrument.

Having thus described the invention, what is claimed as new and desired to be secured by Letters Patent is:

1. An instrument of the character described comprising a iiexible strip; .a planar body having a nose engaging the medial point on the strip; apair of plates rotatably mounted on the body; means for rotating the plates in opposite directions about a common axis; and a plurality of connecting rods joining the plates and said strip for drawing the same into an arched condition as the plates are simultaneously rotated.

2. An instrument of the character described comprising a flexible strip; a planar body having a nose engaging the medial point on the strip between the ends thereof; a pair of plates rotatably mounted on the body; means for simultaneously rotating the plates in opposite directions at the same rate of speed about a common axis; a plurality of connecting rods joining the strip, between said nose and one end thereof, with one of the plates; and a plurality of connecting rods joining the strip, between said nose and the other` end thereof with the other plate whereby when the plates are actuated by the rotating means, the strip is drawn into an arc of a circle.

3. An instrument of the character described comprising a flexible strip; a planar body having a nose engaging the strip intermediate its ends; a pair of plates rotatably mounted on the body; means including an operating lever for simultaneously rotating the plates in opposite directions at the same rate of speed about their axes; a plurality of connecting rods joining the strip, between said nose and one end thereof, with one of the plates; and a plurality of connecting rods joining the strip, between said nloste and the other end thereof with the other p a e.

4. An instrument of the character described comprising a flexible strip; a body having a nose engaging the strip intermediate its ends; a pair of plates rotatably mounted on the body; means for simultaneously rotating the plates in opposite directions at the same rate of speed about a common axis; a plurality of connecting rods joining the strip, between said nose and one end thereof with one of the plates; a plurality of connecting rods joining the strip, between said nose and theY other end thereof, with the other plate; a plurality of scales rotatably mounted for movement with one of said rotatable plates; and a housing for the scales having sight windows formed therein for viewing the scales.

5. An instrument of the character described comprising a flexible strip; a case having a nose engaging the strip intermediate its ends; a pair of plates rotatablycarried by the case; means for simultaneously rotating the plates in opposite directions at the same rate of speed about a common axis; a plurality of connecting rods joining the strip, between said nose and one end thereof, with one of the plates; a plurality of connecting rods, joining the strip between said nose and the other end thereof, with the other plate; and a plurality of scales rotatably mounted for movement with one of said rotatable plates. said case having sight windows formed therein for viewing the scales, each of said scales being arranged to indicate to the operator the degree of the arc described by said strip in relation to a scale of measurement different from the remaining scales.

6. An instrument of the character described comprising a flexible strip; a case having a nose engaging the strip intermediate its ends; a pair of plates rotatably carried by the case; a gear segment on one of the plates; a pinion in mesh with the gear segment; an operating lever for rotating the said one plate; a ,gear segment on the other plate in mesh with the pinion whereby to interconnect the plates for simultaneous movement in opposite directions about a common axis at the same rate of speed; a'

plurality of connecting rods joining the strip between said nose and one end thereof with one of the plates; a plurality of connecting rods joining the strip between said nose and the other end thereof with the other of said plates; and a scale movable as the strip is flexed to indicate the degree of curvature of said strip in relation to a number of scales of measurement.

'7. An instrument of the character described comprising a flexible strip; a case having a nose engaging the strip intermediate its ends; a pair of plates rotatably carried by the case; a gear segment on one of the plates; a pinion in mesh with the gear segment; an operating lever for rotating the said one plate; a gear segment on the other plate in mesh with the pinion whereby to interconnect the plates for simultaneous movement in opposite directions about a common axis at the same rate of speed; a plurality of connecting rods joining the strip between said nose and one end thereof with one of the plates; a plurality of connecting rods joining the vstrip between said nose and the other end thereof with the other of said plates; and a scale movable as the strip is flexed to indicate its degree of curvature, the ends of said connectiong rods 8. An instrument of the character described comprising a exible strip; a body havinganose engaging a point on the strip between the ends thereof; a pair of members rotatably mounted on the body; manually operable means for rotating the plates in opposite directions about a common axis; a plurality of connecting rods joining the plates and said strip for drawing the same against the nose and into an arched condition as the plates are simultaneously rotated; and means for altering the effect of at least one of the connecting rods on the strip as the arm is moved about the axis of rotation with its associated plate.

9. An instrument of the character described comprising a exible strip; a body having a nose engaging a point on the strip between the ends thereof; a pair of members rotatably mounted on the body; manually operable means for rotating the plates in opposite directions about a common axis; a plurality of connecting rods joining the plates and said strip for drawing the same against the nose and into an arched condition as the plates are simultaneously rotated; means slidably mounted on each plate respectively for establishing connection between certain of said arms and the plate; and an element for moving the said means and the associated arms toward and from the axis of rotation as the plates are rotated.

10. In an instrument of the character described, a flexible strip; a plurality of arms each having one end thereof joined to the strip and the other 'ends thereof mounted for wrnovement in paths of travel about a fixed axis; and means for moving said' other ends of said arms toward and fro-m the axis as the same are moved therearound.

SAMUEL MCFARLAND COFFMAN. JAMES EDWIN BELL, JR. 

